Question

I beg your pardon, if its a silly question. But I really need to know how can I use the code I am posting below. I have copied it from a form. I want to implement folder/file icon overlay. So while searching, I found the below code.

public sealed class ShellInterop
    {

        private ShellInterop()
        {
        }
        [DllImport("shell32.dll")]
        public static extern void SHChangeNotify(int eventID, uint flags, IntPtr item1, IntPtr item2);

    }

    [ComVisible(false)]
    [ComImport]
    [Guid("0C6C4200-C589-11D0-999A-00C04FD655E1")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IShellIconOverlayIdentifier
    {

        [PreserveSig]
        int IsMemberOf([MarshalAs(UnmanagedType.LPWStr)]string path, uint attributes);

        [PreserveSig]
        int GetOverlayInfo(
            IntPtr iconFileBuffer,
            int iconFileBufferSize,
            out int iconIndex,
            out uint flags);

        [PreserveSig]
        int GetPriority(out int priority);
    }

    [ComVisible(true)]
    [Guid("B8FA9E43-38E6-4654-8A13-FF905AD22CE5")]
    public class MyIconOverlay : IShellIconOverlayIdentifier
    {

        #region IShellIconOverlayIdentifier Members
        public int IsMemberOf(string path, uint attributes)
        {
            //Show everything with icon overlay
            return 0; // S_OK
        }

        public int GetOverlayInfo(IntPtr iconFileBuffer, int
        iconFileBufferSize,
        out int iconIndex, out uint flags)
        {

            System.Diagnostics.Debug.WriteLine(string.Format("GetOverlayInfo::{0}", iconFileBuffer));

            System.Diagnostics.Debug.WriteLine(string.Format("GetOverlayInfo::{0}", iconFileBufferSize));
            string fname = @"c:\NormalIcon.ico";

            int bytesCount = System.Text.Encoding.Unicode.GetByteCount(fname);

            System.Diagnostics.Debug.WriteLine(string.Format("GetOverlayInfo::{0}", bytesCount));

            byte[] bytes = System.Text.Encoding.Unicode.GetBytes(fname);

            if (bytes.Length + 2 < iconFileBufferSize)
            {
                for (int i = 0; i < bytes.Length; i++)
                {
                    Marshal.WriteByte(iconFileBuffer, i, bytes[i]);
                }
                //write the "\0\0"
                Marshal.WriteByte(iconFileBuffer, bytes.Length, 0);
                Marshal.WriteByte(iconFileBuffer, bytes.Length + 1, 0);
            }

            iconIndex = 0;
            flags = 1; // ISIOI_ICONFILE
            return 0; // S_OK
        }


        public int GetPriority(out int priority)
        {
            priority = 0; // 0-100 (0 is highest priority)
            return 0; // S_OK
        }
        #endregion

        #region Registry
        [ComRegisterFunction]
        public static void Register(Type t)
        {
            RegistryKey rk = Registry.LocalMachine.CreateSubKey(@"SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers\_"
            + t.Name);
            rk.SetValue(string.Empty, t.GUID.ToString("B").ToUpper());
            rk.Close();
            ShellInterop.SHChangeNotify(0x08000000, 0, IntPtr.Zero, IntPtr.Zero);
        }

        [ComUnregisterFunction]
        public static void Unregister(Type t)
        {
            Registry.LocalMachine.DeleteSubKeyTree(@"SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers\_"
            + t.Name);
            ShellInterop.SHChangeNotify(0x08000000, 0, IntPtr.Zero, IntPtr.Zero);
        }
        #endregion
    }

Please if anyone can explain it to me. I have a situation, where I have to implement icon overlay for files and folder that a user creates under a special folder.

Thanks

Answer 1

(edit: fixed regsvr32 to regasm, sorry for my mistake)

This code has three main parts:
1) An interop signature for the IShellIconOverlayIdentifier, the interface used by the shell to add icon overlays.
2) MyOverlay, an implementation of that interface, adding (I’m guessing) the “normalIcon.ico” as the overlay.

3) (this is the important part) code to register and unregister MyOverlay as a shell extension in the registry.

I’m not too familiar with the specifics of icon overlays, but it seems that to enable this you need to call the Register method. Since it’s marked with a [ComRegisterFunction], I’m guessing all you have to do, from a command prompt with admin privileges, is call

C:\> regasm <path to your DLL>

which should call Register. Likewise with regasm /u <path> to uninstall. Give it a try.